The present invention relates to power circuits in general and, in particular, to switching power supply circuits.
Many electronics applications use switching power supplies to convert mains line voltage (e.g., 110-volt, 60-hertz, AC voltage) to a desired application voltage (e.g., 12-volt, DC voltage). Typically, the switching power supply may perform the AC-to-DC conversion by using various controllers to control switching components. Because the controllers need power to operate, it may be necessary to keep them energized even when the application being powered is turned “off” by providing a so-called “standby” mode. The power consumed by the electronics application during its lowest power consumption mode (e.g., in its standby mode) is often called its “standby power” consumption.
In many applications, it may be desirable to reduce power consumption in standby mode, while being able to provide adequate power for consumption when turned “on.” To accomplish this, some power supplies provide auxiliary power components. In standby mode, the power supplies may draw just enough power to energize a controller; but when “on,” the power supply may feedback its output power into an auxiliary power circuit to maintain the controller.
A number of techniques are available in the art for providing auxiliary power. However, these techniques typically add cost and/or complexity to the circuit, for example by using relatively expensive power components like additional transformer windings. As such, it may be desirable to provide power supplies operable to generate auxiliary power with low standby power consumption.